A scroll centrifugal screening machine may be of the type including a housing divided vertically by a dividing wall into an underflow chamber passing to a drain and an overflow chamber passing to an outlet for product. A circular opening through the dividing wall is coaxial with a concentric drive output assembly.
A horizontal centrifugal machine may include a rotating screen assembly having a base portion mounted to an outer output flange of the concentric drive output assembly and closing a narrow end of a conical-section screen formed of a plurality of axially spaced frames interconnected by a plurality of circumferentially spaced stringers and supporting therein a screening surface layer, the outermost one of the frames being located substantially in the plane of and rotating in close proximity to the periphery of the circular opening and defining an open outer end of the screen assembly.
A scroll is mounted to an inner drive shaft of the concentric drive output assembly to be driven differentially (i.e. either a percentage faster or slower) relative to the rotating screen assembly. The scroll includes scraper portions that clear product from the screening surface and impels it toward the open outer end, to fall into the overflow chamber and thence to the gravity outlet.
A source of liquid-entrained material to be screened is delivered through a conduit passing through the open outer end and extending to adjacent the base portion. The conduit may be associated with and supported by a closure member selectively closing a maintenance opening into the housing.
A vertical centrifugal machine may also include a rotating screen assembly having a base of spoke piece portion mounted to an outer output flange of the concentric drive output assembly and secured to the wide end of a conical-section screen formed of a plurality of axially spaced frames interconnected by a plurality of circumferentially spaced stringers and supporting therein a screening surface layer, the outermost one of the frames mounted to the base of spoke piece being located substantially in the plane of and rotating in close proximity to the periphery of the circular opening and defining an open outer end of the screen assembly.
A scroll is again mounted to an inner drive shaft of the concentric drive output assembly to be driven differentially (i.e. either a percentage faster or slower) relative to the rotating screen assembly. The scroll includes scraper portions that clear product from the screening surface and impels it toward the base of spoke piece, to pass therethrough and fall into the overflow chamber and thence to the outlet.
A source of liquid-entrained material to be screened is delivered through a coaxial conduit closely conforming to the narrow inner end of the screen assembly.
In the art of centrifugal screens, there has been an economic tension between long-life components mounting wear components versus more integral assemblies which are changed out as a unit.
Screen assemblies comprised of long-life components mounting wear components represents to a more traditional technology where a heavy, balanced, cast end wall forms the driven, inner end of a horizontal screen assembly, or a “base-of-spoke” piece forms the driven, outer end of a vertical screen assembly. A basket-supporting cage is bolted or set screwed to the end wall or base-of-spoke piece respectively, and the assembly rebalanced. A screening surface assembly is bolted or machine screwed to the cage to forming the rotating part of the centrifugal screen, and the assembly balanced again. The screening surface assembly or the basket supporting cage adjacent the end wall or base of spoke piece, and an outer peripheral portion of the end wall in a horizontal machine, provide a wear resistant zone.
The servicing regime requires setting up craning means to support the assembly, unbolting the end wall or base-of-spoke from the drive flange, extracting the assembly from the screen assembly housing, replacing one or both of the screening surface assembly and cage, rebalancing as assembly progresses and reinstalling the assembly in the housing. The regime assumes that several screening surface assemblies will be replaced before the cage is replaced and that several cages will be replaced before the end wall or base-of-spoke piece is replaced.